class User:
    def __init__(self, first_name, last_name, age, sex):
        self.first_name = first_name
        self.last_name = last_name
        self.age = age
        self.sex = sex

    def describe_user(self):
        print('User profile:')
        print('\t' + 'first name: ' + self.first_name)
        print('\t' + 'last name: ' + self.last_name)
        print('\t' + 'age: ' + str(self.age))
        print('\t' + 'sex: ' + self.sex)

    def greet_user(self):
        print('Hello!' + self.first_name + ' ' + self.last_name + '.')


user_a = User('Albert', 'Einstein', 76, 'male')
user_b = User('Steve', 'Jobs', 56, 'male')
user_c = User('Marie', 'Curie', 67, 'female')
user_a.describe_user()
user_a.greet_user()
user_b.describe_user()
user_b.greet_user()
user_c.describe_user()
user_c.greet_user()
